Inflatable occupant restraint devices for motor vehicles have been under development worldwide for many years. Gas generating compositions for inflating the occupant restraint devices have also been under development for many years and numerous patents have been granted thereon. Because the inflating gases produced by the gas generants must meet strict toxicity requirements, most, if not all gas generants now in use, are based on alkali or alkaline earth metal azides. Sodium azide is presently the preferred fuel for gas generant compositions as it reacts with oxidizing agents to form a relatively non-toxic gas consisting primarily of nitrogen.
A major problem associated with azide based gas generants is the extreme toxicity of the azide itself. The toxicity of the azide based generants makes their use inherently difficult and relatively expensive. In addition, the potential hazard and disposal problems of unfired inflation devices containing azide based generants must be considered.
In contrast the non-azide based gas generants (i.e., 5-aminotetrazole) provide significant advantages over the azide based gas generants with respect to hazards during manufacture and disposal. Unfortunately, the non-azide based gas generants heretofore known produce unacceptably high levels of undesirable substances upon combustion. The most difficult undesirable gases to control are the various oxides of nitrogen (NO.sub.x) and carbon monoxide (CO). An additional problem associated with non-azide based gas generants is the significantly higher combustion temperature relative to the azide based generants.
Gas generants which contain metallic compositions, upon combustion, produce solid particles or what is generally referred to as "slag" or "clinkers" which must be filtered from the combustion gas prior to inflation of the airbag. The ability of a gas generant to form an easily filterable slag is of great advantage when the gases are used for inflation purposes, especially when the gases must be filtered for the inflation of an automobile airbag.
The reduction of the level of undesirable gases upon combustion of non-azide gas generants and the formation of solid combustion particles (slag) requires a special combination of materials. For instance, manipulation of the oxidizer/fuel ratio reduces either the NO.sub.x or CO. More specifically, increasing the ratio of oxidizer to fuel minimizes the CO content upon combustion because the extra oxygen oxidizes the CO to carbon dioxide. Unfortunately, this approach results in increased amounts of NO.sub.x. The relatively high levels of NO.sub.x and CO produced upon combustion of non-azide gas generants and the difficulty presented in forming easily filterable solid combustion products is due, in part, to the relatively high combustion temperatures exhibited by the non-azide gas generants. For example, the combustion temperature of a sodium azide/iron oxide composition can range from about 1,200.degree. C. to about 1,900.degree. C., while the non-azide gas generants exhibit combustion temperatures as high as 2,800.degree. C. Utilizing lower energy fuels to reduce the combustion temperature is ineffective because the lower energy fuels do not provide a sufficiently high rate of gas generation, or burn rate, for use in vehicle restraint systems. Adequate burn rate of the gas generant is required to ensure that the airbag system will operate readily and properly.
The aforementioned problems are solved by the present invention which discloses gas generants that contain from 5-25% by wt. mica. The gas generants of this invention yield easily filterable combustion products and further produce inflating gases at a desired high burn rate while reducing the production of undesired gases. More specifically, this invention relates to non-azide based gas generants that contain up to about 25% by wt. mica.